C.A.H.L.
- YOUR PARTNER IN ANIMAL HEALTH
NEMATODIRUS
IN LAMBS
Nematodirus
battus, if not treated can result in a severe outbreak of disease and
death in young grazing lambs which can have a negative effect on the
profitability of your flock. Nematodirus is generally a spring infection
of lambs. Outbreaks of the disease are most common in May and June.
CAUSE:
Adult female nematodirus worms lay their eggs in the sheep's gut and
the eggs pass out in the faeces and onto the pasture. These eggs take
a very long time to develop, and the larval stages remain inside the
eggshell rather than living free in the sward. Before hatching will
occur the larvae require the stimulus of a cold snap in the weather.
While the infected larvae are well protected inside the eggshell, they
become more vulnerable after hatching and gradually die off if not eaten
by lambs. Young lambs, once grazing are vulnerable to infection. Once
lambs reach three or four months of age they are beginning to become
resistant and by the time they are six months old this resistance is
quite strong. When spring arrives early, the nematodirus eggs hatch
long before the lambs begin to graze, then the great bulk of infected
larvae will have perished before they have the chance to infect the
lambs. With spring lambing flocks, the most dangerous situation is when
spring arrives late, when young lambs of six to eight weeks old are
grazing when the nematodirus eggs hatch. Because the larvae over winter
are inside the egg and hatch simultaneously, they are often present
in massive numbers on the pasture. This ensures that that all lambs
grazing a contaminated field receive an overwhelming dose of larvae
simultaneously. The whole of the lamb flock may begin scouring at the
same time and in the most severe outbreaks the first sign of trouble
may be a number of sudden deaths.
SYMPTOMS:
The damage to the lamb is caused by the large numbers of infected larvae
burrowing into the lining of the gut simultaneously. The symptoms are,
lambs standing with their heads down, ears drooped, belly tucked up
and poor mobility. There is often severe diarrhoea, but because lambs
stop eating, they pass very little other than a slimy mucus. The sunken
eyes and tight skin indicate a severe dehydration, making lambs very
thirsty, so they tend to congregate around the water trough. In severe
cases death is very rapid, whilst other lambs may take several days
to die.
TREATMENT
& PREVENTION:
The nematodirus season frequently coincides with the coccidiosis season,
thus the death rate may rise substantially. Where either of the above
conditions is suspected it is best to seek the professional advice of
your veterinary surgeon. In the event of an outbreak treatment with
an appropriate worm dose must be immediate. Lambs grazing contaminated
pastures should be dosed at three weekly intervals from six weeks of
age until weaning. Prevention is pivotal upon providing grazing for
lambs which were not grazed by lambs during the nematodirus season of
the previous year. The safest pastures are one's with new grass following
ploughing. Pastures grazed in the previous year by adult sheep pose
no risk, since adult sheep are immune to the parasite and carry no adult
nemarodirus worms and do not contaminate the pastures with eggs. Contact
your local CAHL representative for further details.
